Maybe compare its dimensions with those of the MP600/Centerdrive if you or someone you know happen to have one; I can only find open and closed length (7.3" and 4.3" respectively), but not width or depth. Also, you can call/write to their Customer Service since they have a very good service, or at least that has been my experience: I asked them for the fit of that same sheath for an MP600 with needle nose, (since the nylon Centerdrive's sheath wouldn't close secure enough with it inside) and assured me it does fit well and closes; waiting for some expendable income to get it!
Good luck with your search, and enjoy your MP1.